1. Field of the Invention
The present invention relates to a flexible circuit board and particularly to reinforcing structure of the terminal portion thereof.
2. Related Art
With miniaturization of electronic devices, flexible circuit boards that are suitable for the densification of circuitry have been used for general purpose, and various terminal structures for the densified flexible circuit boards have been proposed (see Japanese Patent Laid-Open No. 1994-204636, Japanese Patent Laid-Open No. 1996-37351, Japanese Patent Laid-Open No. 2001-94225, Japanese Patent Laid-Open No. 2002-94203 etc.).
FIGS. 5A and 5B show a terminal portion of a conventional single-side flexible circuit board. The terminal portion needs a certain degree of rigidity, because connector contacts abut on a contact surface 1 formed at a periphery of the board. On that account, reinforcement material 3 is bonded by means of adhesive 2 on a back surface of the contact surface 1 to provide rigidity to the terminal portion.
On the other hand, the densification of circuitry has shifted the type of flexible circuit boards from single-sided to double-sided, so that circuit boards with both sides thereof connected with a connector have been used. In this case, the circuit boards have contact surfaces on both sides of them.
In such double-sided flexible circuit boards, contact surfaces on both sides are offset each other in the longitudinal direction of traces of wiring pattern and reinforcing plates are bonded on the respective back surfaces in order to enhance the rigidity of the board, while the traces of the wiring pattern on the both sides are offset each other in their width direction in order to use the copper foil for reinforcing the rigidity of the board.
However, if the each trace of the wiring pattern of the both front and back sides is positioned on the back surface of the region between the traces of the respective other side in this manner, there is a problem that sufficient contact pressure can not be obtained when connector contacts are pressed onto the traces, because the space resides on the back surface between the traces of the other side.
The present invention is made in consideration of the above-mentioned problem and it is an object of the present invention to improve rigidity of terminals in a double-sided flexible circuit board by using copper foil on an opposite side of the circuit board.